The Supporting Information is available free of charge on the ACS Publications website.Relative carbohydrate composition; detailed mechanical properties of single holocellulose fibers; photograph and microscope image of a single holocellulose fiber fixed on a paper frame;length and diameter distribution of Kraft and holocellulose fibers; stress-strain curves of single holocellulose fibers; photograph of different papers based on Kraft fibers, holocellulose fibers,and fully bleached Kraft fibers